Accelerator pedal device

ABSTRACT

An accelerator pedal device includes: an accelerator pedal; a reaction force application device that applies a reaction force to the accelerator pedal; and a selection device that selects a characteristic between a first characteristic according to a running situation of a subject vehicle and a second characteristic specified regardless of the running situation of the subject vehicle. The first characteristic and the second characteristic each is a characteristic indicating a relationship between an amount of stepping upon of the accelerator pedal and the reaction force to be applied. The reaction force application device applies the reaction force to the accelerator pedal based upon the characteristic selected by the selection device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an accelerator pedal device whichapplies reaction force to an accelerator pedal.

2. Description of the Related Art

In the prior art, return force was applied by a torsion spring to anaccelerator pedal, and a hysteresis effect was generated when theaccelerator pedal was stepped upon and released, so that, as a result, adesired pedal actuation characteristic was obtained.

On the other hand, in Japanese Laid-Open Patent Publication No.H11-78595, there is disclosed a reaction force application device, soconstituted that a reaction force which corresponds to the vehiclerunning environment such as distance between vehicles and the radius ofcurvature of a curved road and the like is applied to the acceleratorpedal via a motor, so as to perform setting of the vehicle speed asappropriate to the vehicle operational environment.

SUMMARY OF THE INVENTION

However, with the above described per se known reaction forceapplication device, it is only possible to generate a reaction forcewhich corresponds to the vehicle running environment, and it has notbeen possible positively to generate hysteresis separately therefrom.

An accelerator pedal device according to the present inventioncomprises: an accelerator pedal; a reaction force application devicethat applies a reaction force to the accelerator pedal; and a selectiondevice that selects a characteristic between a first characteristicaccording to a running situation of a subject vehicle and a secondcharacteristic specified regardless of the running situation of thesubject vehicle. The first characteristic and the second characteristiceach is a characteristic indicating a relationship between an amount ofstepping upon of the accelerator pedal and the reaction force to beapplied. The reaction force application device applies the reactionforce to the accelerator pedal based upon the characteristic selected bythe selection device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system block diagram of a reaction force control devicewhich comprises an accelerator pedal device according to the preferredembodiment of the present invention.

FIG. 2 is a structural view of a vehicle which is equipped with thereaction force control device of FIG. 1.

FIG. 3A is a front elevation view showing the structure of thisaccelerator pedal device according to the preferred embodiment of thepresent invention.

FIG. 3B is a sectional view of a planetary speed reduction mechanism.

FIG. 4 is a side view showing the structure of this accelerator pedaldevice according to the preferred embodiment of the present invention.

FIG. 5 is a figure showing a drive electrical circuit of a servo motorwhich is included in this accelerator pedal device according to thepreferred embodiment of the present invention when the system is notoperating.

FIG. 6 is a figure showing this drive electrical circuit of the servomotor included in the accelerator pedal device according to thepreferred embodiment of the present invention when the system isoperating.

FIG. 7 is a flow chart showing the processing flow of an acceleratorpedal reaction force control program according to the preferredembodiment of the present invention.

FIG. 8 is a figure showing variation of the future speed of the vehiclein front of the subject vehicle.

FIG. 9 is a figure showing the operation of the reaction force controldevice according to the preferred embodiment of the present invention.

FIG. 10 is a figure showing the operation of a different reaction forcecontrol device according to the preferred embodiment of the presentinvention.

FIG. 11 is a figure showing the relationship between accelerator pedalstroke and pedal reaction force, with this preferred embodiment of thepresent invention.

FIG. 12 is a figure showing an example of the accelerator pedal reactionforce characteristic of the accelerator pedal device according to thepreferred embodiment of the present invention when the system isoperating.

FIG. 13 is a figure showing an example of the accelerator pedal reactionforce characteristic of the accelerator pedal device according to thepreferred embodiment of the present invention when the system is notoperating.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following, the preferred embodiment of the accelerator pedaldevice according to the present invention will be explained withreference to FIGS. 1 through 13.

FIG. 1 is a system block diagram of a reaction force control device 1which comprises an accelerator pedal device according to the preferredembodiment of the present invention, while FIG. 2 is a structural viewof a vehicle which is equipped with this reaction force control device1.

First, the structure of the reaction force control device 1 will beexplained. A laser radar 10 is fixed to a grille portion or to a bumperportion or the like at the front of the vehicle, and emits and scanspulses of infrared light in the horizontal direction. Each of aplurality of reflective objects in front of the vehicle (normally therear end of another vehicle in front) reflects back the infrared rays inthese infrared light pulses, and the laser radar 10 measures thesereflected waves and detects the distance to the vehicle in front (thedistance between vehicles) and its relative speed based upon the arrivaltime of the reflected waves. The distance between vehicles and therelative speed which are thus detected are outputted from the laserradar 10 to a controller 50. The region in front of the vehicle which isscanned by the laser radar 10 is the region about ±6° on either side ofthe longitudinal line of the vehicle, and any object which is present infront of the vehicle in this region is detected in this manner. And avehicle speed sensor 20 detects the running speed of the subject vehiclefrom the rotational speed of a wheel thereof or the like, and outputsthis running speed to the controller 50. The subject vehicle means avehicle to be controlled with the reaction force control.

The controller 50 calculates the degree of proximity to the vehicle infront which is running in front of the subject vehicle from the speed ofthe subject vehicle which are inputted from the vehicle speed sensor 20and the distance between vehicles and the relative speed which areinputted from the laser radar 10, and estimates the current runningsituation of the subject vehicle. This running situation includes thestate of the subject vehicle itself and the environmental statesurrounding the subject vehicle. Furthermore it estimates how thisrunning situation will change in the future, and outputs a reactionforce command value to an accelerator pedal reaction force controldevice 60.

The accelerator pedal reaction force control device 60 controls thetorque which is generated by a servo motor 70 which controls theaccelerator pedal reaction force, according to the amount of actuationof the accelerator pedal 80 which is detected by a stroke sensor 71.According to the command value of the accelerator pedal reaction forcecontrol device 60, the torque which is generated by the servo motor 70can be controlled, so that the reaction force which is generated whenthe driver actuates the accelerator pedal 80 can be controlled asdesired.

FIGS. 3A and 4 are respectively an elevation view and a side viewshowing the structure of the accelerator pedal device according to thispreferred embodiment of the present invention. The accelerator pedal 80comprises a pedal 80 to which the driver applies foot pressure, and alever 82 which supports this pedal 81. The lever 82 is rotatablysupported via a bearing 84 upon a base plate 83 which is fixed to thevehicle body. The one end of a tension spring 85 is linked to the lever82 via a bracket 86, and the other end of this tension spring 85 islinked to the vehicle body via a bracket 88. The spring force of thistension spring 85, which corresponds to the amount of actuation of theaccelerator pedal 80, acts upon the accelerator pedal 80 as a reactionforce. The stroke sensor 71 is, for example, an angular sensor whichdetects the amount of rotation of a rotational shaft 82 a, and whichdetects the stroke S of the accelerator pedal 80 based upon thisdetected value. The stroke S of the accelerator pedal 80 corresponds tothe amount of actuation of the accelerator pedal 80.

The rotational shaft 82 a of the lever 82 is linked to the output shaft70 a of the servo motor 70 via a planetary speed reduction mechanism 87.In other words, a carrier 87 d is integrally provided upon the tip ofthe rotational shaft 82 a, and three planetary gears 87 a are supportedupon this carrier 87 d so as to be rotatable. Along with a ring gear 87b which is provided so as not to be rotatable being meshed with theseplanetary gears 87 a, they are also meshed with a sun gear 87 c which isintegrally formed upon the output shaft 70 of the motor 70 (refer to thecross sectional view b—b of FIG. 3B). Accordingly, it is also possiblefor the torque of the servo motor 70 to act upon the accelerator pedal80 as a reaction force, in addition to the spring reaction force due tothe tension spring 85. Here, the tension spring 85 and the servo motor70 constitute a reaction force application means.

A drive circuit for the servo motor 70 is shown in FIGS. 5 and 6. Anelectric current control circuit 72 is connected to the servo motor 70via an operation changeover relay 73. This current control circuit 72outputs an electrical current i according to the command value of theaccelerator pedal reaction force control device 60. An ON signal isoutputted from the accelerator pedal reaction force control device 60 tothe coil of the operation changeover relay 73 when the system isoperating, while an OFF signal is outputted thereto when the system isnot operating. The relay contact points 73 a and 73 b are opened andclosed by this ON/OFF signal, so that the characteristic of the reactionforce F with respect to the stroke S of the accelerator pedal 80 ischanged over between a first characteristic and a second characteristicwhich will be explained hereinafter. It should be understood that thisoperation changeover relay 73 constitutes a selection means.

Next, the operation of this reaction force control device 1 according tothe preferred embodiment of the present invention will be explained. Thesummary of this operation is as follows.

The controller 50 recognizes the running situation or state such as thedistance between vehicles (the distance to the vehicle in front of thesubject vehicle), their relative speed, and the running vehicle speed ofthe subject vehicle, and, based upon this running situation, calculatesthe present degree of proximity to the vehicle in front (a first risklevel), and the degree of influence upon the subject vehicle due to thetrend of the future movement of the vehicle in front as predicted fromthe present (a second risk level). Furthermore, the controller 50predicts the future running situation or state (a risk potential RP)from the degree of proximity and the predicted degree of influence whichhave thus been calculated, calculates an accelerator pedal. reactionforce command value ΔF based upon this risk potential RP, and outputsthis command value ΔF to the accelerator pedal reaction force controldevice 60. The accelerator pedal reaction force control device 60controls the servo motor 70 according to this command value ΔF, andthereby the stroke reaction force characteristic of the acceleratorpedal 80 is changed.

For example, with the stroke S—pedal reaction force F characteristic asshown in FIG. 11, the reaction force characteristic in the normal state,in other words when the accelerator pedal reaction force control is notbeing performed by the reaction force control device 1 (i.e. when thesystem is not operating), is endowed with a hysteresis when theaccelerator pedal 80 is stepped upon and is released, as shown by thedotted portion in the figure. Due to this, it is possible to keep thepedal stroke S constant even if the force by which the pedal is steppedupon varies by a certain amount, so that the maintainability of thepedal stroke S is enhanced.

On the other hand, during reaction force control (i.e. when the systemis operating), an accelerator pedal reaction force F is generated whichis increased over the reaction force characteristic during the normalstate by just the accelerator pedal reaction force command value ΔF. Dueto this, the reaction force F of the accelerator pedal 80 comes to bedetermined according to the risk potential RP, and it is possible tocause the present and the future predicted running situation of thevehicle to be recognized by the driver of the vehicle via thisaccelerator pedal reaction force F. In this case, in order for the riskto be accurately sensed by the driver, it is desirable for the system tobe endowed with a straight line characteristic with no hysteresis, asshown in FIG. 12.

In the following, the manner in which the accelerator pedal reactionforce command value is determined when the accelerator pedal reactionforce control is being performed will be explained with reference to theflow chart shown in FIG. 7. It should be understood that FIG. 7 is aflow chart showing the processing flow of an accelerator pedal reactionforce control program which is performed by the controller 50. The stepsof this procedure are performed repeatedly in sequence at a fixed timeinterval (for example 50 msec).

The Processing Flow of the Controller 50 (FIG. 7)

First in the step S110 the vehicle running state, comprising the speedVf of the subject vehicle, the distance D between vehicles to thevehicle in front, the relative speed Vr, and the speed of the vehicle infront Va, as detected by the laser radar 10 and the vehicle speed sensor20, are read in.

In the next step S120, based upon this vehicle running state which hasbeen read in, the present degree of proximity to the vehicle in frontand the predicted degree of influence upon the subject vehicle due tochange in the surrounding environment from now on are calculated. Here,a time to contact between vehicles TTC is calculated as the degree ofproximity to the vehicle in front, while a time headway between vehiclesTHW is calculated as the predicted degree of influence. The time tocontact between vehicles TTC may be referred to as a clearance timeperiod between vehicles and the time headway between vehicles THW may bereferred to as a time period between vehicles. In the following, thiscalculation of the time to contact between vehicles TTC and the timeheadway between vehicles THW will be explained.

The time to contact between vehicles TTC is a physical quantity thatgives the current degree of proximity of the subject vehicle withrespect to the vehicle in front. This time to contact between vehiclesTTC is a value which gives whether or not, after a few seconds, if thepresent running situation is maintained, in other words if the subjectvehicle speed Vf, the speed of the vehicle in front Va, and the relativevehicle speed Vr remain constant, the distance between vehicles D willbecome zero and the subject vehicle and the vehicle which is running infront of it will come into mutual contact; and it is obtained accordingto the following Equation (1):Time to contact between vehicles TTC=D/Vr  (Equation 1)

The smaller is the value of the time to contact between vehicles TTC,the more acute is the contact with the vehicle in front, and this meansthat the degree of proximity to the vehicle in front is great. Forexample, when the subject vehicle approaches towards the vehicle infront, it is known that almost every driver will have started to performdeceleration operation before the time to contact between vehicles TTCbecomes less than 4 seconds. Although, in this manner, the time tocontact between vehicles TTC is a quantity which exerts a greatinfluence upon the driving performance of the driver, it is difficult toexpress the risk which the driver feels with respect to contact with thevehicle in front only by this time to contact between vehicles TTC.

For example, if the subject vehicle is running so as just to track afterthe vehicle in front without catching it up, then its relative vehiclespeed Vr with respect to the vehicle in front is 0, and the time tocontact between vehicles TTC is infinitely large. However in this casethe risk which the driver feels is different if the distance betweenvehicles D is long or if it is short, and in fact the driver feels thatthe risk is the greater, the shorter is the distance between vehicles D.This is considered to be because the driver predicts the amount ofinfluence upon the time to contact between vehicles TTC which will becaused by the variation in the future of the vehicle speed of thevehicle in front which he hypothesizes, and feels the risk to be thegreater, if he recognizes that this influence is large.

Furthermore, with the time to contact between vehicles TTC which hasbeen calculated according to Equation (1), it has been supposed that therelative speed Vr is constant, but actually there is a possibility thatafter Δt seconds the relative speed Vr will have changed. For example,it is not of course possible to predict the running speed Va of thesubject vehicle accurately after Δt seconds, but it is possible topredict that it will be endowed with some deviation such as that shownin FIG. 8. Here, when the vehicle running speed V2 after Δt seconds hasbecome slower than the current vehicle running speed V1, along with thisthe relative vehicle speed Vr changes, and the time to contact betweenvehicles TTC after Δt seconds has a smaller value as compared with whatwould be the case if the relative vehicle speed Vr remained constant, sothat the risk as felt by the driver is higher. However, it is difficultto determine this from the time to contact between vehicles TTC whichhas been calculated based upon the current relative vehicle speed Vr.Thus, apart from the time to contact between vehicles TTC, if thesubject vehicle is running so as just to track after the vehicle infront, the degree of influence upon the time to contact between vehiclesTTC due to variation of the future vehicle speed of the vehicle in frontwhich is hypothesized, in other words the degree of influence when ithas been assumed that the relative vehicle speed Vr changes, iscalculated. As the physical quantity which expresses the predicteddegree of influence upon the time to contact between vehicles TTC, thetime headway between vehicles THW which is given by one or the other ofthe following Equations (2) and (3) is used:Time headway between vehicles THW=D/Va  (Equation 2)Time headway between vehicles THW=D/Vf  (Equation 3)

This time headway between vehicles THW is the distance between vehiclesD divided by the running speed of the vehicle in front Va or by thespeed Vf of the subject vehicle Vf, and it represents the time perioduntil the subject vehicle arrives at the current position of the vehiclein front. The greater is this time headway between vehicles THW, thesmaller does the predicted degree of influence with respect to changesof the surrounding environment become. In other words, if the timeheadway between vehicles THW is great, even if in the future the vehiclespeed of the vehicle in front changes, this will not exert a greatinfluence upon the degree of proximity of the subject vehicle to thevehicle in front, so that the time to contact between vehicles TTC willnot exhibit any very great change.

It should be understood that, since the time headway between vehiclesTHW is a value which expresses the degree of influence due to changes ofthe vehicle speed of the vehicle in front in the future, Equation (2)which uses the running speed Va of the vehicle in front is in betteraccordance with the risk which is experienced by the driver, thanEquation (3) which uses the running speed of the subject vehicle Vf.However, since the running speed Va of the vehicle in front iscalculated from the speed of the subject vehicle Vf and the relativevehicle speed Vr, accordingly it is possible to calculate the timeheadway between vehicles THW more accurately from Equation (2) whichuses the subject vehicle speed Vf, which is detected with high accuracyby the vehicle speed sensor 20. It should be understood that, if thesubject vehicle is running so as just to track after the vehicle infront, then Equation (2) is the same as Equation (3), since the subjectvehicle speed Vf is equal to the running speed Va of the vehicle infront.

In the step S120 above, the time to contact between vehicles TTC and thetime headway between vehicles THW are calculated. Next, in the stepS130, the predicted future situation (the risk potential RP) iscalculated based upon the time to contact between vehicles TTC and thetime headway between vehicles THW which have thus been calculated in thestep S120. This risk potential RP is given by the following Equation(4), and is a physical quantity which is given continuously as the sumof the degree of proximity to the vehicle in front (1/TTC) and thepredicted degree of influence upon the future situation (1/THW), asadjusted by certain coefficients.RP=a/THW+b/TTC  (Equation 4)

It should be understood that a and b are respective parameters forappropriately weighting the degree of proximity and the predicted degreeof influence, and they are suitably set, with a<b. It is desirable forthe values of a and b to be estimated from statistics relating to thetime headway between vehicles THW and the time to contact betweenvehicles TTC, and they may, for example, be set to values around a=1 andb=8.

It should be understood that, as will be understood from the abovedescribed Equations (1) through (3), the time to contact betweenvehicles TTC is the risk level regarding how many seconds the subjectvehicle will take to come into contact with the vehicle in front, whenit is assumed that the relative speed Vr between the vehicle in frontand the subject vehicle is constant, while the time headway betweenvehicles THW is the risk level regarding how many seconds the subjectvehicle will take to arrive at the current position where the vehicle infront is located, when it is assumed that the relative speed Vr betweenthe vehicle in front and the subject vehicle will change in the future.This time to contact between vehicles TTC and time headway betweenvehicles THW are individually calculated from the present subjectvehicle speed Vf, the speed Va of the vehicle in front, and the relativevehicle speed Vr, but it is possible to estimate the risk potential RPwhich is predicted for the future by adjusting these using Equation (4).

The risk potential RP is possible to correspond to the continuous changeof the situation from tracking after the vehicle in front untilapproaching to the vehicle in front, and it is possible to express thedegree of proximity in these circumstances. In other words, it ispossible to determine that, the greater is the risk potential, thegreater does the driver feel the risk of perhaps coming too close to thevehicle in front in the future to be.

In FIG. 9, the risk potential RP which is calculated from Equation (4)is shown, in a planar chart of the time headway between vehicles THWagainst the reciprocal of the time to contact between vehicles (1/TTC),as each line has each value of the risk potential RP. In FIG. 9, thetime headway between vehicles THW is shown along the horizontal axis,and the reciprocal (1/TTC) of the time to contact between vehicles TTCis shown along the vertical axis; and, the more to the right along thehorizontal axis, the farther is the subject vehicle running from thevehicle in front, while, the more upwards along the vertical axis, thecloser is the subject vehicle to the vehicle in front, while the lowertherealong, the farther is it removed from the vehicle in front. In FIG.9, each line of equal risk potential RP is drawn as a smooth line fromthe upper right to the lower left, and the value of the risk potentialRP changes continuously between these lines of equal risk potential. Itshould be understood that the smaller is the time headway betweenvehicles THW and the greater is the reciprocal 1/TTC of the clearancetime period, i.e. the more to the upper left of FIG. 9, the greater isthe value of the risk potential RP. In other words, the closer to thevehicle in front and the greater is the degree of proximity thereto, thehigher does the value of the risk potential RP assume. Furthermore, evenif the degree of proximity 1/TTC has the same value, the shorter is thetime headway between vehicles THW, the greater does the value of therisk potential RP become.

In the step S131, a decision is made as to whether or not the riskpotential RP which has been calculated in the step S130 is greater thana predetermined value. If it is decided that the risk potential RP isgreater than the predetermined value, then the flow of control istransferred to the step S132. In the step 132, a signal to turn on theoperation changeover relay 73 is output (the state of FIG. 6), and theflow of control is transferred to the step S140. In the step 131, if itis decided that the risk potential RP is not greater than thepredetermined value, then the flow of control is transferred to the stepS133. In the step 133, a signal to turn off the operation changeoverrelay 73 is output (the state of FIG. 5), and the control is terminated.In the step S131 through the step S133, it is decide or selected basedupon the risk potential RP according to the running situation of thevehicle whether or not the control explained below to apply a reactionforce corresponding to the reaction force command value ΔF is performed.

In the step S140, the accelerator pedal reaction force command value ΔFis calculated according to the following Equation (5), based upon thevalue of the risk potential RP which was calculated in the step S130:ΔF=K·RP  (Equation 5)Here, K is a constant value which should be set appropriately.

As shown in FIG. 9, the risk potential RP is given continuously forevery running situation as defined by the time headway between vehiclesTHW and degree of proximity 1/TTC. By calculating the accelerator pedalreaction force command value ΔF using Equation (5), and by controllingthe accelerator pedal reaction force according to the risk potential RP,it becomes possible to ensure that the degree of proximity to thevehicle in front is continuously recognized by the driver.

Next, in the step S150, the accelerator pedal reaction force commandvalue ΔF which was calculated in the step S140 is outputted to theaccelerator pedal reaction force control device 60, and then thisepisode of processing terminates.

In the step S130 described above, the value of the risk potential RP wascalculated by weighting the present degree of proximity (1/TTC) and thepredicted degree of influence (1/THW) individually and adding togetherwith them using Equation (4). By doing this, it is possible to obtainthe risk potential RP continuously even if the present degree ofproximity or the predicted degree of influence change, and it ispossible continuously to change the accelerator pedal reaction forcewhich is set in correspondence to this risk potential RP. And it ispossible for the driver accurately to recognize changes in the runningsituation of the vehicle from the accelerator pedal reaction force whichchanges smoothly and continuously.

It should be understood that the risk potential RP may also becalculated as shown in the following Equation (6):RP=max{a/THW, b/TTC}  (Equation 6)

In this case, as shown in Equation (6), the value of the maximum oneamong the degree of proximity (the reciprocal of TTC) to the vehicle infront and the predicted degree of influence (the reciprocal of THW) inthe future state is selected as the value of the risk potential RP. Itshould be understood that a and b are parameters for weighting thedegree of proximity and the predicted degree of influence respectively,and, for example, they may be appropriately set to around a−1 and b=8,with a<b. By doing this, it is possible to correspond to continuouschange of the situation from tracking after the vehicle in front untilapproaching to the vehicle in front, and it is possible to express thedegree of proximity in these circumstances.

In FIG. 10, the risk potential RP which is calculated from Equation (6)is shown, in a planar chart of the time headway between vehicles THWagainst the reciprocal of the time to contact between vehicles (1/TTC),as each line has each value of the risk potential RP. In FIG. 10, justas in FIG. 9, the time headway between vehicles THW is shown along thehorizontal axis, and the reciprocal (1/TTC) of the time to contactbetween vehicles TTC is shown along the vertical axis. As shown in FIG.9, when calculating the risk potential RP using the above describedEquation (4), at times such as when the relative speed Vr is negative sothat the vehicle in front is moving faster than the subject vehicle andis getting farther away from it, even if the time headway betweenvehicles THW has the same value, the risk potential RP becomes extremelysmall. Along with this, the accelerator pedal reaction force commandvalue ΔF also undesirably becomes extremely small.

On the other hand, in the value of the risk potential RP which has beencalculated using Equation (6), the greater one of the present degree ofproximity to the vehicle in front (1/TTC) and the predicted degree ofinfluence (1/THW) in the future is selected. Due to this, even if thedegree of proximity (1/TTC) is negative, in other words even if therelative vehicle speed is negative, the value of the risk potential RPdoes not drop below a predetermined value which is determined by thetime headway between vehicles THW, as shown in FIG. 10. It should beunderstood that the time headway between vehicles THW is the time periodfor the subject vehicle to arrive at the current position of the vehiclein front, so that it can never have a negative value. Due to this, whenthe risk potential RP is calculated by using the above Equation (6), itis possible to prevent sudden change of the value of the risk potentialRP, which would cause an undesirable sudden change of the acceleratorpedal reaction force.

With this reaction force control device 1 according to this preferredembodiment of the present invention, the present degree of proximity tothe vehicle in front (the time to contact between vehicles TTC) and thedegree of influence due to change of the surrounding environment of thevehicle which is predicted for the future (the time headway betweenvehicles THW) are calculated, and these are added together withindividual weightings in order to calculate the risk potential RP. And,by additionally applying a force which is proportional to this riskpotential RP to the accelerator pedal reaction force, it becomespossible to control the reaction force of the accelerator pedal basedupon a value which is close to the risk level which is actually felt bythe driver of the vehicle. If the present degree of proximity to thevehicle in front is great (i.e. if the time to contact between vehiclesTTC is small), or if the degree of influence for the future which ispredicted is great (i.e. if the time headway between vehicles THW issmall), then the risk potential RP becomes great, and a greataccelerator pedal reaction force is generated in proportion to thisrelatively great risk potential RP. Due to this, when the degree ofproximity to the vehicle in front is great so that the risk potential RPis great, the driver, who is stepping down upon the accelerator pedal80, is induced towards releasing the accelerator pedal 80.

In concrete terms, by increasing the accelerator pedal reaction force,the driver is caused to recognize from this increased amount of reactionforce the fact that the risk potential has increased, and by his owndecision he is enabled to actuate (to release) the accelerator pedal toa satisfactory state. Furthermore, by increasing the accelerator pedalreaction force, the foot of the driver who is stepping down upon theaccelerator pedal is naturally returned towards the release side, sothat it is led towards a more satisfactory state, even though the driverdoes not particularly notice this fact. Yet further, since, byincreasing the accelerator pedal reaction force, the necessary steppingupon force which is required when further stepping down upon theaccelerator pedal from its current state of depression becomes greater,accordingly it is possible to restrain the driver from increasing thespeed of the subject vehicle by further stepping down upon theaccelerator pedal, so that it is possible to suppress further reductionof the distance between vehicles to the vehicle in front.

Moreover, if the accelerator pedal reaction force command value ΔF isdetermined based upon the risk potential RP which has been calculatedusing Equation (4), the risk potential RP changes continuously as shownin FIG. 9. Due to this, it is possible to cause the driver to recognizethe vehicle running situation which corresponds to the degree ofproximity 1/TTC to the vehicle in front and to the time headway betweenvehicles THW, via the accelerator pedal reaction force which iscontinuously transmitted to him. Furthermore, if the risk potential RPis calculated using Equation (6), the risk potential changes as shown inFIG. 10. Due to this, even if the vehicle in front accelerates away fromthe subject vehicle so that the degree of proximity 1/TTC becomesextremely small, it is still possible to perform accelerator pedalreaction force control in a stabilized manner, since the risk potentialRP never changes abruptly.

Yet further, since the time to contact between vehicles TTC and the timeheadway between vehicles THW can be calculated using physical quantitieswhich are each comparatively easy to calculate, such as the subjectvehicle speed Vf, the speed of the vehicle in front Va, the distancebetween vehicles D, and the like, accordingly it is possible to suppressincrease in the number of component parts which are required for theconstruction of this driving actuation assistance device for a vehicle.Moreover, when setting the parameters a and b for calculation of therisk potential RP, by setting the parameter b for the time to contactbetween vehicles TTC to be greater than the parameter a for the timeheadway between vehicles THW, it is possible to calculate the riskpotential while giving greater weighting to the present degree ofproximity to the vehicle in front than to the degree of influence due tochange of the surrounding environment of the vehicle in the future.

Next, the details of the operation of the accelerator pedal deviceaccording to this preferred embodiment of the present invention will beexplained.

(1) When the System is Operating

The laser radar 10 of the subject vehicle detects the vehicle in front,and the reaction force control system starts to operate when the riskpotential exceeds a predetermined value. Due to the operation of thissystem, the coil of the operation changeover relay 73 is supplied withelectrical current as shown in FIG. 6, and the contact points 73 a ofthis relay 73 are closed, while its contact points 73 b are opened. Thecontroller 50 calculates the risk potential RP with respect to thevehicle in front as has been previously described, and the acceleratorpedal reaction force control device 60 controls the output of theelectric current control circuit 72 according to this calculated riskpotential RP. Due to this, the torque of the servo motor 70 iscontrolled, and a motor torque reaction force ΔF which corresponds tothe risk potential RP is additionally applied to the accelerator pedal80 by being added to the reaction force which is produced by the tensionspring 85.

An example of the reaction force F which is applied to the acceleratorpedal 80 is shown by the characteristic f1 of FIG. 12. It should beunderstood that this characteristic f1 is a first characteristic, whilethe characteristic f0 in the figure is the reaction force characteristicof the tension spring 85 which serves as the base for this firstcharacteristic f1. Since there is no sliding portion in the tensionspring 85 such as is present in a torsion spring, the frictional forceis smaller than if a torsion spring were to be employed. As a result,the generation of hysteresis is suppressed, and the spring reactionforce which serves as a base changes in a linear manner, as shown by thecharacteristic f0.

Furthermore, since as described above the output shaft 70 a of the servomotor 70 and the rotational shaft 82 a of the accelerator pedal 80 arearranged via the planetary speed reduction mechanism 87 as being almostcoaxial, therefore the mechanical loss is smaller as compared with thecase of using a bevel gear or a worm gear or the like, so that theproportion of the torque which is transmitted is greater. As a result,it is possible to apply a reaction force ΔF to the accelerator pedal 80which corresponds to the risk potential RP with good accuracy, and thegeneration of hysteresis is suppressed, so that the reaction force Fwhich is applied to the accelerator pedal 80 changes in a linear manneras shown by the characteristic f1. It should be understood that it wouldalso be possible to arrange the output shaft 70 a of the servo motor 70and the rotational shaft 82 a of the accelerator pedal 80 almostcoaxially without using the planetary speed reduction mechanism 87.

By providing a reaction force characteristic in this manner in which thefrictional force of the spring and the mechanical loss of the gears issmall so that there is no substantial hysteresis, the driver is enabledeasily to sense the risk of approach to the vehicle in front. In otherwords, if the reaction force characteristic were to have hysteresis asshown by the dotted line in FIG. 12, even if a reaction force ΔFcorresponding to the risk potential were to be applied to theaccelerator pedal 80, it would be difficult for the driver accurately toapprehend the degree of risk, since there would be a danger that hemight misunderstand the increase of the reaction force due to theinfluence of such hysteresis. By contrast to this, if the reaction forcecharacteristic is linear, the driver can recognize the increase ofreaction force as the increase of the risk directly, and he is ableaccurately to sense the risk of perhaps getting too close to the vehiclein front in the future.

(2) When the System is not Operating

When, for example, the laser radar 10 is not detecting any vehicle infront of the subject vehicle, the risk potential is below thepredetermined value, and the reaction control system does not operate.When this system is not operating, as shown in FIG. 5, the supply ofelectric current to the coil of the operation changeover relay 73 isinterrupted, and the contact points 73 a of this relay 73 are opened,while its contact points 73 b are closed. Due to this, both of theterminals of the servo motor 70 are grounded. In other words, both ofthe terminals are shorted. If at this time the accelerator pedal 80 isstepped down upon or is released, the output shaft 70 a of the servomotor 70 is rotated according to this pedal actuation, and an inducedelectromotive force is generated in this servo motor 70.

This induced electromotive force acts as a viscous force so as to impedethe actuation of the accelerator pedal 80. As a result, if theaccelerator pedal 80 is stepped down upon or is released, as shown inFIG. 13, the pedal reaction force F exhibits a second characteristicwhich is endowed with hysteresis. In other words, when at the time pointa in FIG. 13 the accelerator pedal 80 is stepped down upon, theaforementioned viscous force is added to the spring reaction force (thecharacteristic f2), and the pedal reaction force F is increased as shownby the arrow sign. On the other hand, when at the time point a in FIG.13 the accelerator pedal 80 is released, the return of the acceleratorpedal 80 is checked by the viscous force, and the pedal reaction force Fdiminishes as shown by the arrow sign. By generating hysteresis in thepedal reaction force F in this manner, it is possible to maintain thepedal stroke amount S constant even if the force with which theaccelerator pedal 80 is stepped upon varies a little, and the driver isable easily to perform adjustment of the speed of the vehicle.

If a breakdown has occurred in the reaction force control system (forexample, if one of the signal lines has broken), the supply of operatingelectrical current to the coil of the operation changeover relay 73 isinterrupted. Since due to this the reaction force characteristic becomesone which is endowed with hysteresis, it becomes easy for the driver toadjust the stroke of the accelerator pedal 80, so that the actuatabilityis good. It would also be possible, for example, for a signal to beinputted into the operation changeover relay 73 from a failure diagnosedevice not shown in the figure, and for this failure diagnose device tointerrupt the supply of operating electrical current to the coil of theoperation changeover relay 73 if it should detect a failure or amalfunction.

With the accelerator pedal device of the preferred embodiment of thepresent invention as described above, the following beneficial effectsare obtained.

-   (1) The operation changeover relay 73 of the servo motor 70 is    changed over according to whether the reaction force control system    is operating or is not operating; and, when the system is operating    (for example when a vehicle is present in front of the subject    vehicle), the torque of the servo motor 70 is controlled, while,    when the system is not operating (for example when no vehicle is    present in front of the subject vehicle), no such torque control is    performed, and the servo motor 70 is set so as to perform    self-induction. By doing this, it is possible to apply reaction    force to the accelerator pedal in two different patterns, and the    management of these patterns is easy. In other words, it is possible    to apply reaction force selectively either with a characteristic in    which hysteresis is absent or is only present to a small degree, or    with a characteristic which is endowed with substantial hysteresis,    so that, by applying such reaction force properly according to    circumstances, the convenience of use can be enhanced.-   (2) Since the tension spring 85 and the servo motor 70 are linked to    the accelerator pedal 80, and it is arranged to apply the spring    reaction force and the motor torque reaction force to the    accelerator pedal 80, thereby, along with it being possible to apply    by such motor torque control a pedal reaction force ΔF which    corresponds to the risk potential, it is also possible to apply a    pedal reaction force so as to generate hysteresis by taking the    spring reaction force as a reference.-   (3) Since the reaction force is applied to the accelerator pedal 80    using the servo motor 70, it is possible to perform the reaction    force control accurately.-   (4) Since the output shaft 70 a of the servo motor 70 and the    rotational shaft 82 a of the accelerator pedal 80 are arranged    almost coaxially via the planetary speed reduction mechanism 87, it    is possible to reduce the mechanical loss in the gears, and it is    possible to suppress the generation of hysteresis during reaction    force control.-   (5) Since it is arranged to perform electrical current control of    the servo motor 70 during operation of the system, while when the    system is not operating both the terminals of the servo motor 70 are    short circuited together, accordingly, although electrical current    control of the servo motor 70 is not performed when the system is    not operating, it is possible easily to provide a hysteresis    characteristic.-   (6) Since the tension spring 85 is used as a return spring for the    accelerator pedal 80, the frictional force is reduced as compared    with the case of use of a torsion spring, so that it is possible to    suppress the generation of hysteresis by the return spring itself    during reaction force control.

The accelerator pedal device according to the present invention is notto be considered as being limited to the above described preferredembodiment; various modifications are possible. For example, although inthe above description a reaction force characteristic having hysteresiswhen the system was not operating was provided by self-induction of theservo motor 70, it would also be possible to provide such a hysteresischaracteristic by a signal from the electrical current control circuit72. In such a case, it is desirable to calculate the speed of theactuation of the accelerator pedal 80 by time differentiation of itsactuation as detected by the stroke sensor 71, and to control the torqueof the servo motor 70 so as to apply a reaction force which isproportional to this calculated actuation speed.

Moreover, although in the shown preferred embodiment of the presentinvention the reaction force was applied to the accelerator pedal 80 bythe use of the servo motor 70, it would also be possible to apply such areaction force by the use of some other type of actuator, provided thatit was one which could adjust the applied reaction force as desired.Furthermore, although in the shown preferred embodiment it was arrangedduring system operation to perform reaction force control according tothe risk potential, it would also be possible to apply some type ofcontrol other than one according to the risk potential to theaccelerator pedal device of the present invention to some other type ofcontrol, provided that it was one in which reaction force control was tobe performed according to the vehicle operational state or the runningenvironment in the surroundings of the vehicle. Yet further, althoughduring reaction force control it is desirable to apply reaction force ina no hysteresis state, it is not absolutely necessary for no hysteresisat all to be applied during such reaction force control. Finally, ratherthan the tension spring 85, it would also be possible to employ a springmember which had some other structure.

In the above described embodiment, it is selected by executing the stepS131 through the step S133 in FIG. 7 whether or not the reaction forcecorresponding to the reaction force command value ΔF is applied.However, the step S131 through the step S133 may be deleted. In thiscase, the electric current control circuit 72 is always connected to theservo motor 70. And when the substantial zero value of the reactionforce command value ΔF is calculated, the characteristic in which thereaction force corresponding to the reaction force command value ΔF isnot applied is substantially selected.

The above described embodiments are examples, and various modificationscan be made without departing from the spirit and scope of theinvention.

The disclosure of the following priority application is hereinincorporated by reference:

-   -   Japanese Patent Application No. 2002-180005 filed Jun. 20, 2002.

1. An accelerator pedal device for a vehicle, comprising: an acceleratorpedal; an accelerator pedal reaction force control device forcontrolling reaction force to be applied to the accelerator pedal; aselection device for selecting a first characteristic or a secondcharacteristic of reaction force to be applied to the accelerator pedal;and a reaction force application device, responsive to the selectiondevice, for applying reaction force to the accelerator pedal accordingto the first characteristic while the accelerator pedal reaction forcecontrol device is activated and applying reaction force to theaccelerator pedal according to the second characteristic while theaccelerator pedal reaction force control device is inactive; wherein atleast said first characteristic is determined by the accelerator pedalreaction force control device as a function of a running situation ofthe vehicle and the operating condition of the vehicle; and wherein oneof said first characteristic and said second characteristic hassubstantially less hysteresis than the other of said firstcharacteristic and said second characteristic.
 2. An accelerator pedaldevice according to claim 1, wherein: the selection device selects acharacteristic between the first characteristic and the secondcharacteristic based upon the running situation of the subject vehicle.3. An accelerator pedal device according to claim 1, wherein: the firstcharacteristic is a characteristic to apply the reaction force withsubstantially no hysteresis corresponding to the amount of stepping uponof the accelerator pedal; and the second characteristic is acharacteristic to apply the reaction force with hysteresis correspondingto the amount of stepping upon of the accelerator pedal.
 4. Anaccelerator pedal device according to claim 3, wherein: the secondcharacteristic is specified so that a reaction force to be applied whenthe amount of stepping upon of the accelerator pedal start to becomegreater at a predetermined amount of stepping upon of the acceleratorpedal is greater than reaction force to be applied when the amount ofstepping upon of the accelerator pedal become smaller at thepredetermined amount of stepping upon of the accelerator pedal.
 5. Anaccelerator pedal device according to claim 1, wherein: the firstcharacteristic is a characteristic in which a reaction force specifiedaccording to the running situation of the subject vehicle is added to areaction force according to the second characteristic.
 6. An acceleratorpedal device according to claim 5, wherein: the reaction forceapplication device calculates, based upon the running situation of thesubject vehicle, a degree of proximity to a vehicle in front at thepresent time and a degree of influence upon the subject vehicle due to atrend of movement of the vehicle in front predicted in the future, andcalculates the reaction force to be added to the reaction forceaccording to the second characteristic based upon the calculated degreeof proximity and the degree of influence.
 7. An accelerator pedal deviceaccording to claim 1, wherein the reaction force application devicecomprises: a spring member that applies a first reaction forcecorresponding to the amount of stepping upon the accelerator pedal; andan actuator that applies a second reaction force additionally to thefirst reaction force by the spring member according to the runningsituation of the subject vehicle when the first characteristic isselected, and applies a third reaction force in a hysteresis manneradditionally to the first reaction force by the spring member when thesecond characteristic is selected.
 8. An accelerator pedal deviceaccording to claim 7, wherein: the accelerator pedal is rotatable arounda rotational shaft; and the actuator is a servo motor that applies atorque reaction force to the rotational shaft of the accelerator pedal.9. An accelerator pedal device according to claim 8, wherein: an outputshaft of the servo motor and the rotational shaft of the acceleratorpedal are arranged via a gear mechanism, as being substantially coaxial.10. An accelerator pedal device according to claim 8, wherein: theselection device outputs a control electrical current to the servo motoraccording to the running situation of the subject vehicle when the firstcharacteristic is selected, and substantially shorts both terminals ofthe servo motor when the second characteristic is selected.
 11. Anaccelerator pedal device according to claim 7, wherein: the springmember is a tension spring whose one end is linked to the acceleratorpedal, while its other end is linked to a body of the vehicle.
 12. Avehicle, comprising: an accelerator pedal; an accelerator pedal reactionforce control device for controlling reaction force to be applied to theaccelerator pedal; a selection device for selecting a firstcharacteristic or a second characteristic of reaction force to beapplied to the accelerator pedal; and a reaction force applicationdevice, responsive to the selection device, for applying reaction forceto the accelerator pedal according to the first characteristic while theaccelerator pedal reaction force control device is activated andapplying reaction force to the accelerator pedal according to the secondcharacteristic while the accelerator pedal reaction force control deviceis inactive; wherein at least said first characteristic is determined bythe accelerator pedal reaction force control device as a function of arunning situation of the vehicle and the operating condition of thevehicle; and wherein one of said first characteristic and said secondcharacteristic has substantially less hysteresis than the other of saidfirst characteristic and said second characteristic.
 13. A method forcontrolling reaction force to be applied to an accelerator pedal by anaccelerator pedal reaction force control device, comprising the steps:selecting a first characteristic or a second characteristic of reactionforce to be applied to the accelerator pedal; applying reaction force tothe accelerator pedal according to the first characteristic while theaccelerator pedal reaction force control device is activated; applyingreaction force to the accelerator pedal according to the secondcharacteristic while the accelerator pedal reaction force control deviceis inactive; and determining at least the fist characteristic as afunction of a running situation of the vehicle and the operatingcondition of the vehicle; wherein one of said first characteristic andsaid second characteristic has substantially less hysteresis than theother of said first characteristic and said second characteristic.